Device and method for making devices comprising at least a chip fixed on a support

ABSTRACT

A method for mounting, on a support, at least a microcircuit in the form of a chip produced on a very thin semiconductor substrate. An interconnection point is provided at the chip in the form of a bump contact in weldable material. The bump contact has a welding surface in the same plane as at least one of the chip faces. An interconnection pad is provided on the support that is designed to be welded with a corresponding bump contact of the chip. The welding face of each bump contact of the chip is placed opposite each corresponding interconnection pad of the support. Each bump contact of the chip is welded with each corresponding interconnection pad of the support. The method can be applied to a device such as a chip card.

This disclosure is based upon French Application No. 99/07551, filed onJun. 15, 1999 and International Application No. PCT/FR00/01490, filedMay 30, 2000, which was published on Dec. 21, 2000 in a language otherthan English, the contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to a device and a method for manufacturingelectronic devices containing at least one chip fixed to a support.

In certain fields, including that of smart cards, it is necessary toeffect the mounting of a microcircuit or chip on a relatively thin andflexible support. In the case of smart cards, it is necessary on the onehand for the presence of the chip not to cause an excessive thicknessbeyond a threshold established by international standards (currentlyfixed at 50 μm) and on the other hand for the mounting of the chip to besufficiently secure to allow durable use even when the card is subjectedto relatively high bending and twisting stresses.

In a conventional manner, the creation of an excessive thickness isavoided by housing the chip in a cavity provided for this purpose in thethickness of the support.

FIG. 1 schematically shows a known example of mounting a chip 6 on asupport 2 intended to constitute a smart card. The chip 6 is housedalmost entirely in a cavity 3 so that its thickness is included withinthat of the support 2. The chip 6 has a set of connecting pads 5 on theedges of its surface turned towards the outside of the cavity 3. Thesepads 5 are connected to respective contacts 7 on the support by wires 9.The contacts 7 can be situated at the bottom of the cavity, or at anintermediate level in a recessed area 11 around the cavity, as in theexample illustrated. These contacts 7 are in their turn electricallyconnected to contact areas 13 intended to allow an ohmic connection witha card reader. These contact areas 13 are housed entirely in the recess11 so that their thickness is also contained within that of the support2.

To protect the whole, a coating of protective material 15 is formed,covering the entire area occupied by the cavity 3, the wires 9 and aportion of the internal edges of the contact areas 11.

This conventional technique suffers from several drawbacks. Firstly, theoperation consisting in electrically connecting the connecting pads 5 ofthe chip 6 to the contacts 7 requires the use of very fine and delicatewires 9, thus forming fragile points. Moreover, the operations ofsoldering these wires 9 requires a significant amount of tooling and anot insignificant amount of time.

Moreover, the formation of the cavity 3 requires a machining step whichis both expensive and weakening for the card.

It should also be noted that this technique based on the integration ofa chip in a cavity in a support is difficult to use when it is necessaryto connect together several components, for example several chips orother passive or active elements on the same support.

In addition, it is important to design methods which are compatible withautomated tooling for mass production, allowing high rates of attachingand welding chips.

SUMMARY OF THE INVENTION

In the light of these problems, the present invention proposes a methodfor mounting at least one microcircuit in the form of a chip on asupport, characterised in that it includes, for the chip or chips, thefollowing steps:

a) providing a chip produced as a very thin semiconductor having atleast one interconnection point in the form of a contact pad made fromweldable material, said pad having a welding face substantially in thesame plane as at least one of the faces of the said chip;

b) providing, at the support, at least one interconnection area intendedto be welded with a corresponding contact pad on the chip;

c) placing the welding face of the contact pad or pads on the said chipopposite the corresponding interconnection area or areas on the support;and

d) welding the contact pad or pads on the said chip with thecorresponding interconnection area or areas on the support.

The present invention advantageously uses the technology of chipsproduced in a very thin substrate, as described notably in the patentdocument WO-A-9802921 in the name of Kopin. This technology notablymakes it possible to dispose chips having a thickness of 10 microns, oreven very substantially less than this thickness.

Advantageously, the interconnection area of the support is produced on aportion of a surface of a face of the support situated in the generalplane of this face. In other words, no cavity or recess is created foraccommodating the thickness of this interconnection area. Because ofthis, the interconnection area and also the chip project with respect tothe overall plane of the face on which they are situated. Thisarrangement is possible, by virtue of the invention, because a chipespecially configured according to the definition in paragraph a) aboveis provided.

Preferably the contact pad or pads are produced in aluminium.

Likewise, it is also possible to produce the interconnection area orareas in aluminium.

The method according to the invention lends itself notably to welding bythermocompression or ultrasound.

According to a first embodiment of the invention, the contact pad orpads of the chip pass through the thickness of the chip so as to have asurface accessible on each of the faces of the chip.

This arrangement notably makes it possible to perform the welding stepby transmission of energy through the pad or pads in the direction ofthe thickness of the chip. In other words, the energy for the welding isapplied to the face of the contact pad situated opposite to the weldingface.

According to one advantageous aspect of this embodiment, a protectivesubstrate which holds the chip is also provided at step a). The weldingstep can then be performed after the removal of this substrate from thechip.

According to a second embodiment of the invention, a protectivesubstrate with a first face which holds a set of chips is also providedat step a).

Before the welding step, cuts are made around at least one chip on theprotective substrate, with a depth of cut which reaches at least thefirst face of the substrate. After the welding step, the support withits welded chip or chips is separated from the protective substrate. Thefact that the cuts have previously been made around the chip makes itpossible to remove it in its cut form. It is then possible to performthe aforementioned cuts in the form of notches which pass only partiallythrough the thickness of the protective substrate. In this case, thesubstrate for all the chips on a wafer remains whole, which facilitatesthe removal of the chips after welding.

Advantageously, according to this second embodiment, at least when thesupport is separated, the protective substrate is held so as to enablethe chip to be removed by peeling when the support is separated.

The substrate can be held by the interposing of an adhesive layerbetween a second face thereof, opposite to the first, and a base.

According to a variant of this second embodiment, the depth of cutcompletely passes through the protective substrate. This arrangement ispossible when the protective substrate can be fixed firmly to its base,for example by means of the aforementioned adhesive layer.

The present invention also relates to a device, such as a smart card,having at least one microcircuit in the form of a chip mounted on asupport and connected to at least one interconnection area for thesupport, characterised in that the chip or chips have at least onecontact pad having a surface for contact with a corresponding contactarea on the support, the contact surface being, at one face of the chip,opposite the contact area.

Advantageously, the contact surface of the contact pad is substantiallyon the same plane as the face of the chip opposite the saidinterconnection area.

Preferably, the interconnection area of the support is produced on aportion of a surface of a face of the support which is situated in theoverall plane of this face.

The contact pad or pads can be produced from aluminium.

According to a first embodiment of the device, the contact pad or padspass through the thickness of the chip.

Advantageously the chip has an excess thickness relative to the overallplane of the face of the support on which it is attached equal to orless than 50 microns.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and its advantages will emergemore clearly from a reading of a preferred embodiment, given purely byway of non-limitative examples, with reference to the accompanyingdrawings, in which:

FIG. 1, already described, is a view in section of a known smart cardshowing the location of a chip in a cavity in the support;

FIG. 2 is a partial plan view of a wafer resulting from the so-calledsilicon on insulator technology used in the embodiments of theinvention;

FIG. 3 is a view in section of an assembly composed of a very thin chip,a protective substrate and adhesive pads according to the so-calledsilicon on insulator technology;

FIG. 4 is a schematic view in section showing the operation of attachingthe chip illustrated in FIG. 3 on its support according to a firstembodiment of the invention; and

FIGS. 5a to 5 c are schematic views in section showing successiveoperations of preparing a wafer containing very thin chips producedaccording to the so-called silicon on insulator technology and ofattaching these chips to a support according to a second embodiment ofthe invention.

DESCRIPTION OF THE INVENTION

FIG. 2 is a view which shows a wafer 12 resulting from the so-calledsilicon on insulator (SOI) technology. This technology makes it possibleto produce chips 2—that is to say the active part of themicrocircuit—which are very thin.

The SOI technology for obtaining chips with such dimensionalcharacteristics is described notably in the patent document WO-A-9802921 in the name of Kopin. Thus the manufacturing details will not berepeated for reasons of conciseness.

The chips 2 are disposed in lines of rows on an insulating protectivesubstrate 4, typically glass, which constitutes the body of the wafer.This insulating substrate 4 serves amongst other things to protect thechips 2, which are flexible because of their thinness (around 10microns).

Each chip 2 is held on the protective glass substrate 4 by adhesive pads6. These adhesive pads 6 consist of small rectangular areas, turnedthrough 45° with respect to the sides of the chips 2 and placed on therespective corners of each chip, so that, apart from the periphery ofthe wafer 12, a pad 6 covers four joined corners of four differentchips.

FIG. 3 shows an assembly 10 after cutting of the wafer 12 intoelementary surfaces each comprising a chip 2. The assembly 10 thuscomprises the chip itself 2, its protective substrate 4 to thedimensions of the chip and the adhesive pads 6 holding the chip on thesubstrate by its corners.

The chip 2 is provided with interconnection pads 8 which make itpossible to communicate between the circuit which it contains and theexternal environment of the circuit, notably with regard to input andoutput signals and a supply voltage.

These pads 8 are produced by areas of conductive material, in this casealuminium. Because of the great thinness of the chip 2—its thicknessdoes not exceed 100 microns and is in the example around 5 microns—it ispossible to produce the interconnection pads so that they have a contactsurface on each face 2 a and 2 b of the chip 2. In other words, eachinterconnection pad passes through the thickness of the chip 2, as shownin FIG. 3.

In the example illustrated, the contact faces 8 a and 8 b of theinterconnection pads are substantially flush with the respective faces 2a and 2 b of the chip 2. However, these contact faces 8 a and 8 b can beslightly recessed or projecting vis-à-vis these respective faces 2 a and2 b whilst being considered to be substantially on the overall plane ofthe corresponding face 2 a, 2 b of the chip. These connection pads aredistinguished from those known in the form of protrusions (also referredto as “bumps” in English terminology) which have an appreciableprotuberance vis-à-vis the plane of the chip, this protuberance beingprecisely used to create the interconnection.

The protective substrate 4 and the adhesive pads 6 serve essentially toprotect the chip during manufacture and handling before the chip isattached to its final support.

FIG. 4 shows a step of attaching a chip 2 after the removal of theprotective substrate 4 and the adhesive pads 6, according to a firstembodiment of the invention. In this first embodiment, the removal ofthe protective substrate takes place through an operation of peeling offthe latter before the step of final fixing of the chip.

The bare chip 2 is then attached to its communication interface 14produced at the surface of its support 16. This communication interface4 can, according to the applications envisaged, serve to:

connect inputs and outputs of the chip with the outside, notably thecontact card readers; and/or

provide the necessary interconnections between the chip and the elementsproduced at the support. These elements can be an antenna integratedinto the support 2 so as to constitute a so-called “contactless card”,known per se, other circuit elements integrated into the card (forexample one or more other chips), or an electric supply source.

In the embodiment, the communication interface 14 is produced bymetallisations intended to provide different electrical connectionsbetween the chip and the elements associated with the support 16. Thesemetallisations converge towards the location of the support intended toreceive the chip 2 whilst having connection areas 14 a. Each connectionarea 14 a of the communication interface is situated vertically in linewith a respective contact pad 8 on the chip 2. At least the part of thecommunication interface which comprises the connection areas 14 a isproduced from aluminium.

Once the chip is positioned vis-à-vis the connection areas 14 a, awelding is effected in order to connect the latter with the respectivepads 8 on the chip. It should be noted that the contact pads 8 arethrough pads; the chip can be attached to its support 16 with one orother of its faces 2 a or 2 b turned towards the latter. In the example,the faces 8 b of the contact pads are opposite the connection areas 14a.

The welding is carried out by means of a thermocompression tool whichsupplies a pressure to the face 8 a of the contact pad opposite to theone 8 b turned towards the connection area 14 a. To this end, thethermocompression tool has a welding head 18 a with a cross-sectionsubstantially equal to or less than the surface of the contact pad 8,intended to come against the surface 8 a of the latter and press the padagainst its corresponding connection area 14 a. At the same time, thetool 18 supplies heat energy by generating vibrations through the pad 8.This energy raises the temperature at the contact point and generatesthe fusion of the contact pad 8 with its connection area 14 a. It shouldbe noted that these two connection elements 8 and 14 a, both being madefrom aluminium, are perfectly compatible with this thermocompressiontechnique.

The thermocompression technique is well-known per se and will not bedetailed here for reasons of conciseness.

In a variant, it can also be envisaged effecting the welding of theconnection points 8 and 14 a by ultrasound or laser beam according totechniques known per se. In these cases also, the welding energy can beapplied to the face 8 a of the pad 8 opposite to the one 8 b in contactwith the connection area and thus pass through the thickness of the pad.

Naturally, it is possible to envisage producing the contact pads 8and/or the connection areas in other metals or alloys provided that theyare compatible with the manufacturing techniques and welding used.

The use of contact pads 8 which are substantially without relief withrespect to the respective faces 2 a and 2 b of the substrate, that is tosay without a protrusion, makes it possible notably to effect automatedwelding according to the technique known by the English term “bumplesstape automatic bonding” or “bumpless TAB”. This technique makes itpossible to effect welding at very high rates by mounting the chips 2 ona tape which is made to pass in front of the welding tool 18, thesupport 16 also being passed in synchronism with the welding rate.

A second embodiment of the invention will now be described withreference to FIG. 5, for also welding very thin chips provided withbumpless contact pads. These chips have to a great extent the samecharacteristics as those described in the first embodiment. Thus onlythe differences will be described here for reasons of conciseness.

As shown by FIG. 5a, the chips 2 are provided with connection pads 8which have only one contact surface, present on the face 2 a turnedtowards the outside vis-à-vis the protective glass substrate 4. As withthe first embodiment, these contact pads have substantially no reliefrelative to the face 2 a on which they are present, being producedaccording to the so-called “bumpless” technology to use the Englishterm. In the example, the pads 8 are also produced from aluminium,although other electrically conductive materials can be envisagedaccording to compatibility with the welding technique provided.

According to the second embodiment, a cutting of the assembly 10including the chip 2, the adhesive pads 6 and part of the thickness ofthe substrate 4 is effected. This partial cutting is carried out bymeans of a cutting tool 20, such as a rotary blade, which forms, at eachspace 22 separating two adjacent chips 2, a notch 24 perpendicular tothe overall plane of the wafer 12. Each notch 24 passes through anadhesive pad 6 (and possibly a portion of the unused edge of the chip 2)and a part of the protective glass substrate 4. The termination point 24a of each notch is not critical, provided that it is situated at leastbelow the level of the bottom surface 2 b of the chips and above theface 4 a of the substrate opposite to the one 4 b opposite the chips 2.

It should be noted that the notches 24 are formed on a grid whichdivides the chips 2 into lines and rows on the wafer 12 (FIG. 2). Thuseach of the four edges of a chip 2 is surrounded by a notch 24.

Once the notches 24 have been made, the face 4 a of the wafer 12 isplaced on a platform 26 so that the wafer is held thereon fixedly. Thisfixing can be obtained by mechanical means of fixing the wafer and/or bythe interposing of an adhesive between the platform 26 and the face 4 aof the glass substrate 4. By way of example, the platform 26 can beprovided on its top face (which receives the wafer 12) with an adhesivefilm 26 a (FIG. 5c). The assembly including the wafer 12 with thenotches 24 is then ready for an operation of attaching the chips to thesupport for which the chips are intended (film, card, printed circuit,grid, etc).

In the example, the support 16 is the same as for the case of the firstembodiment. As shown in FIG. 5c, this support also has metallisationsformed on the surface, the ends of which converge in order to formconnection areas 14 a in aluminium or another material compatible withthe welding technique used, each connection area being intended to beconnected with a corresponding pad 8 on the chip 2.

The support 16 as shown is in the form of a continuous strip which willbe cut into individual devices (for example smart cards) once thewelding operation has ended.

In order to effect the welding between the pads 8 on the chips 2 and thecorresponding connection areas 12 on the supports, use is made of athermocompression tool 18 as described previously in the context of thefirst embodiment.

Each pad 8 on a chip 2 is matched with its corresponding connection area14 a under the head 18 a of the thermocompression tool. This arrangementis obtained by running under it the strip forming the support 16 in thedirection of the arrow d and the correlated movement of the platform 26holding the wafer 12. The head 18 a of the thermocompression tool 18 issituated just above the face 16 b of the support opposite to the one 16a intended to receive a chip 2.

As shown in FIG. 5c, the strip forming the support 16 follows a curvedpath and stands proud of the wafer 12 at the point where the latter issituated at a tangent, vertically in line with the thermocompressiontool. At this point, a pad 8 on the chip is situated opposite thecorresponding connection area 14 a formed on the support 16. Thethermocompression tool 18 then performs the welding of the pad 8 withthe connection area 14 a by applying energy through the thickness of thesupport 16 and the pad 8.

For each chip 2 thus welded to its support, the path of the strip movesit away from its protective substrate 4. There is thus created a forceof pulling away or cleaving the chip 2 from its protective substrate 4.The latter, because it is held on its platform, enables the chip to bedisconnected from the adhesive pads 6 when it is moved away from thesubstrate. This is because the adhesion between the pads 8 and theconnection areas 14 a is substantially higher than the adhesive pads 6.Likewise, the adhesion of the adhesive pads 6 is substantially less thanthe breaking strength of the substrate 4, even when weakened by thenotches 24. It should be noted that, when the chip 2 is disconnectedfrom its protective substrate 4, the adhesive pads 6 remain on thelatter.

It will be understood that the notches 24 serve essentially to separatethe edges around each chip 2. The fact that they partially breach thethickness of the protective substrate 4 does not play a decisive role inthe welding process which has just been described. This is because thethickness of the protective substrate 4 is partially breached onlybecause the current cutting techniques do not make it possible toexactly limit the depth of the cut to the thickness of the chip, whichcan be substantially less than 10 microns. Thus the notch in thethickness of the substrate is due to the tolerance in the precision ofthe cutting tool 20.

According to a variant of the second embodiment, the wafer 12 is cutcompletely at the locations of the notches 24, so that each portion ofprotective substrate 4 around a chip 2 is mechanically disconnected fromthe remainder of the wafer 12. The assembly thus cut is maintained inits configuration before cutting by the adhesive film 26 a. In thisvariant, the cleaving force occasioned by the removal of the support 16with the welded chips 2 is entirely countered, at the protectivesubstrate 4, by the adhesive force of the film 26 a.

Naturally, the second embodiment and its variant also make it possibleto use other welding techniques, such as ultrasonic welding, laser beamwelding, etc.

For the first and second embodiments, it is possible to provide asubsequent step of deposition of a protective layer on at least theexposed parts of the chip or chips on their support. This deposition canbe effected by attaching a fine film or by spraying a lacquer.

Naturally, the scope of the present invention extends to allapplications requiring an attachment of a very thin chip on a surface ofa support, this being able to be not only flexible (film, sheet, plasticcard, etc) but also rigid.

What is claimed is:
 1. A method for manufacturing an electronic devicehaving at least one chip and a support, comprising the steps of:providing a thin chip having a thickness which does not exceed 100 μmand at least one contact pad made from a weldable material that issubstantially flush with at least one face of said chip; providing asupport with at least one communication interface having at least oneinterconnection area protruding in its overall plane; placing said oneface of the chip against the surface of the support so that the contactpad comes into direct contact with the communication interface; andwelding the contact pad with the corresponding communication interfaceof the support, by applying welding energy through the thickness of thesupport and/or through the pad.
 2. A method according to claim 1 whereinthe contact pad passes through the thickness of the chip in order topresent a welding surface on each of two opposite faces of the chip, andthe chip is welded to the interconnection area by applying weldingenergy through the thickness of the pad.
 3. A method according to claim1 wherein the welding step is carried out by thermocompression,ultrasound or laser beam, through the thickness of the pad.
 4. A methodaccording to claim 1 wherein the support is made from a materialcompatible with the technique used for welding, and the welding step iseffected by thermocompression, ultrasound or laser beam, through thethickness of the support.
 5. A method according to claim 1 wherein thechip has a thickness of about 5 μm.
 6. A method according to claim 1,wherein said chip is disposed on a protective substrate.
 7. A methodaccording to claim 6, further including the step of removing thesubstrate prior to the step of welding.
 8. A method according to claim6, wherein the placing step and the welding step are effected before astep of removal of the substrate.
 9. A method according to claim 6,wherein the protective substrate has a first face which holds a set ofchips; and before the welding step notches are cut in the protectivesubstrate around the chip, a point of termination of the depth of thenotch in the substrate being situated at least below the level of abottom face of the chip.
 10. A method according to claim 9 wherein,after the welding step, the support with its welded chip is separatedfrom the protective substrate.
 11. A method according to claim 9wherein, before the welding step, the support with the set of chips isseparated from the protective substrate.
 12. A method according to claim9 wherein the protective substrate is held so as to allow the removal ofthe chip by peeling off.
 13. A method according to claim 9 wherein thenotches pass completely through the thickness of the protectivesubstrate.
 14. A method according to claim 9 further including a stepsubsequent to that of welding of removing the protective substrate anddepositing a thin protective layer on at least the exposed parts of thechip and its support.
 15. A method according to claim 9, wherein saidnotches terminate at a depth that is above a face of the substrate whichis opposite to the face on which said chip is disposed.
 16. The methodof claim 1, wherein said electronic device is a smart card, and saidcommunication interface comprises a contact for connecting input and/oroutput signals of the chip with a card reader.
 17. The method of claim1, wherein said electronic device is a contactless smart device, andsaid communication interface comprises an antenna.
 18. The method ofclaim 17, wherein said smart device is a smart card.
 19. An electronicdevice in the form of a smart card, having at least one chip and asupport, said chip having at least one contact pad made from weldablematerial; the support having at least one communication interface weldedto the contact pad which is in direct contact with the communicationinterface, wherein the chip has a thickness between its faces that doesnot exceed 100 μm and is attached to the communication interfacevertically in line with the contact pad; and the support has at leastone interconnection area projecting in its overall plane without anycavity or recess for accommodating this area.
 20. A device according toclaim 19, wherein the support is made from a material compatible withthe application of welding energy through the thickness of said support.21. A device according to claim 20, wherein the welding surface of thecontact pad is substantially on the same plane as the face of the chipadjacent the interconnection area.
 22. A device according to claim 19wherein the chip has a thickness equal to or less than 50 μm.
 23. Adevice according to claim 19 wherein the interconnection area isconnected to at least one element of the input and output interface witha contact reader and/or antenna reader, on the surface of the support.24. A device according to claim 19, wherein the contact passes throughthe thickness of the chip to present a welding surface on each of twoopposite faces of the chip.
 25. A device according to claim 19 whereinthe chip has a thickness of about 5 μm.
 26. The device according toclaim 19, wherein said communication interface comprises a contact forconnecting input and/or output signals of the chip with a card reader.27. The device according to claim 19, wherein said smart card is acontactless card, and said communication interface comprises an antenna.